In low-voltage electrical circuits and low-voltage systems, or rather low-voltage networks, i.e. circuits for voltages up to 1000 V AC voltage or 1500 V DC voltage, short circuits are usually associated with the occurrence of arc faults, such as parallel or serial arc faults. In high-power distribution and switchgear systems in particular, if these are not shut down sufficiently quickly this can lead to irretrievable damage to equipment, system parts or entire switchgear systems. To prevent long-lasting and widespread failure of the power supply and to reduce personal injuries, it is necessary to detect and extinguish such arc faults, in particular high-current or parallel arc faults, within a few milliseconds. Conventional protection systems of power supply systems (e.g. fuses and circuit breakers) cannot provide reliable protection under the required time constraints.
Here, circuit breakers are in particular meant to refer to low-voltage switches. Circuit breakers, in particular in low-voltage systems, are usually used for currents from 63 to 6,300 amperes. More particularly, sealed circuit breakers, such as molded case circuit breakers, are used for currents from 63 to 1600 amperes, in particular from 125 to 630 or 1200 amperes. Open circuit breakers, such as air circuit breakers, are used in particular for currents from 630 to 6300 amperes, more particularly from 1200 up to 6300 amperes.
Circuit breakers in the sense of the invention can in particular comprise an electronic trip unit, abbreviated to ETU.
Circuit breakers monitor the current flowing through them and interrupt the electrical current or energy flow to an energy sink or a consumer, a process known as tripping, if current limit values or current time interval limit values, i.e. if a current value is present for a certain period of time, are exceeded. The determination of the tripping conditions and the tripping of a circuit breaker can be performed by way of an electronic trip unit.
Earthing switches are special devices for short-circuiting cables or power rails, in order to produce defined short circuits for the protection of electrical circuits or systems.